The invention is based on a fuel injection pump as a set forth hereinafter. In one such fuel injection pump, known from German Patent Disclosure DE 44 40 749, the injection adjuster piston with one face end encloses the first pressure chamber in the cylinder and with its other face end encloses a spring chamber, which is pressure-relieved, in the cylinder. The control slide is provided in the injection adjuster piston and is actuatable by a control piston. With one end, this control piston protrudes into the second pressure chamber that receives the compression a spring, and the control piston acts upon the control slide counter to the force of a restoring spring that engages the control slide. On the other end, in a part structurally connected to the housing and separate from the second pressure chamber, the control piston is acted upon by a control pressure that adjusts the control piston counter to a restoring spring, whereupon the control slide follows along with the adjustment of the control piston under the influence of the restoring spring.
For adjusting the injection adjuster piston, the first pressure chamber is acted upon by a pressure fluid that is controlled by the adjustment of the control slide relative to the control piston and that is supplied to the control slide via a radial bore in the injection adjuster piston. To that end, there is also a pressure fluid inlet in the circumferential wall of the cylinder, and this pressure fluid inlet communicates constantly with a groove extending in the adjusting direction of the control piston, from which the radial bore leads to the cylinder bore that receives the control slide. The injection adjuster piston is thus acted upon by forces because of the unilateral inlet of the pressure fluid. Furthermore, through a recess in the cylinder wall, there is a communication with a pump interior in which the cam drive is located. This cam drive, with an actuating arm, reaches through this recess into a corresponding indentation of the injection adjuster piston, so that the injection adjuster piston, in the course of its longitudinal motion, can effect a rotation of the cam drive. From this side, a unilateral pressure relief of the injection adjuster piston is accomplished. In this known pump, complicated means must be provided with which the unilateral stresses on the injection adjuster piston are compensated for, to prevent disruptions in operation caused by wear. In particular, if the injection adjuster piston is connected eccentrically to the associated cam drive, forces additionally enter from the side of the cam drive and act in the form of tilting moments on the injection adjuster piston, consequently leading to increased unilateral, local pressures between the jacket face of the injection adjuster piston and the cylinder guide receiving it.
According to the fuel injection pump of the invention, it is attained that the injection adjuster piston is acted upon by high adjusting pressure only in the axial direction and is not exposed to any radially acting force components that would entail the aforementioned risk. The force exerted on the injection adjuster piston by the second pressure chamber serves as a constant base stress, which counteracts the restoring force in the first pressure chamber. The restoring forces of the restoring means in the first pressure chamber also act exclusively axially on the injection adjuster piston. Furthermore, the chamber receiving the cam drive is embodied as a relief chamber, so that in operation of the mechanical connection of the cam drive, which connection is realized in the form of an actuating arm, to the adjusting piston, once again there is no high pressure acting radially on the injection adjuster piston. The injection adjuster piston is thus loaded evenly by its adjusting means. Accordingly, the frictional forces and thus the wear between the injection adjuster piston and its cylinder wall receiving the adjuster piston are reduced.
Advantageous refinements of the invention are shown with their advantages in conjunction with the ensuing description of an exemplary embodiment.